WASHINGTON (AFP) – The US government urged police and the public to be on high alert Monday for possible terrorist plots to avenge slain Al-Qaeda chief Osama bin Laden, warning Western targets around the world were at risk.
CIA director Leon Panetta, a key architect of the daring US special forces raid that left bin Laden dead at a secretive Pakistan compound, warned "terrorists almost certainly will attempt to avenge him."
"We must -- and will -- remain vigilant and resolute," Panetta said, as concerns about retaliation tempered exuberant celebrations of bin Laden's slaying nearly 10 years after the September 11, 2001 attacks.
In New York, where Al-Qaeda suicide operatives used passenger airplanes as guided missiles to destroy the World Trade Center Towers, beefed-up police patrols carried assault rifles at "Ground Zero" and subway stations.
"As of now, there are no new immediate threats against our city. But there is no doubt we remain a top target, and the killing of Bin Laden will not change that," cautioned New York City Mayor Michael Bloomberg.
In Washington, flocks of tourists strolled past the marble-domed US Capitol, as police tasked with lawmakers's safety deployed what they described as "enhanced security measures" there and at congressional office buildings.
"The public may notice an increased police presence and enhanced patrols in the field -- and some measures may not even be visible to the public," said a spokeswoman, Sergeant Kimberly Schneider.
US Homeland Security Secretary Janet Napolitano said authorities were "at a heightened state of vigilance" as her agency issued a private message to security personnel nationwide darkly warning of possible attacks.
"The Intelligence Community (IC) assesses the death of Al-Qaeda leader Osama bin Laden could result in retaliatory attacks in the Homeland and against US and Western interests overseas," it said in the bulletin, which AFP obtained.
The department said attacks could originate among core Al-Qaeda members in Pakistan's remote tribal areas, among the group's overseas affiliates, or individuals who are not members but who identify with the extremist network.
"Overseas, the strongest reaction is expected to be in South Asia but will likely occur to differing degrees worldwide, including Europe," warned the department, which was created after the September 11, 2001 attacks.
"Other high-risk regions include those where Al-Qaeda's affiliates and allies have operational strongholds, including the Middle East, Africa, and Southeast Asia," it said in the message.
US intelligence "lacks current insight into Al-Qaeda's selection of Homeland targets, but as seen in previous Al-Qaeda core plotting symbolic, economic, and transportation targets could be at risk," the department warned.
"Small-arms attacks against soft targets, which could be perceived as more achievable than other types of attacks, cannot be ruled out," it said, noting it had "no indications of advanced Al-Qaeda core plotting efforts" on US soil.
But bin Laden's death may lead Al-Qaeda operatives to "accelerate" planning for attacks in the United States and "may provide justification for radicalized individuals in the United States to rapidly mobilize for attacks here."
US authorities "are on what I would describe as an unofficial high alert for the natural reason that they worry there's going to be a retaliatory attack," Senate Homeland Security Committee Chairman Joseph Lieberman told reporters.
"Thank God, so far they have no specific or credible evidence" he said, stressing that "we need everybody in America to follow the 'see something, say something' rule" of telling police about suspicious activity.
Lieberman said he had been briefed by Napolitano earlier about her decision not to issue a new terrorism alert, citing the lack of precise information about a threat.
In Los Angeles, authorities reportedly tightened security at area airports and other potential targets and urged the public to report any suspicious activity.